code: def test_update_alpha(old_arr, alpha_start_arr, new_arr):
      _update_alpha(
          old_arr, starting_array=alpha_start_arr
      )  # this operation is in-place
      assert np.array_equal(old_arr, new_arr)
  
imports: import pytest
  import numpy
  from eli5.base import Explanation, TargetExplanation
  from eli5.formatters.image import format_as_image, heatmap_to_image, expand_heatmap, _validate_heatmap, _update_alpha, _cap_alpha, _overlay_heatmap
  from .utils_image import assert_pixel_by_pixel_equal
label_desc: Use image node_id 12 for calling a global function with example usage: test_update_alpha(old_arr, alpha_start_arr, new_arr) without return types